The present invention is directed to oxygen breathing apparatus. It finds particular application in high-altitude terrain in which sub-freezing temperatures are expected.
Systems for supplementing the oxygen breathed by climbers have been employed in Himalayan mountaineering expeditions for some time. Most have been of the open-circuit, compressed-oxygen type. These systems allow the climber to operate more efficiently both mentally and physically than he would without the system.
With open-circuit systems, however, it is not feasible to raise the partial pressure of the oxygen in the lungs to that of air at sea level. Furthermore, the oxygen in such systems must be stored under high pressure, typically between 3500 and 4500 psi. This requires the use of pressure-reduction devices that have not always been reliable. Additionally, the use of high-pressure systems for military applications is not desirable because of the possibility that the pressure vessel could be pierced by projectiles, thereby exposing the soldier using the system to the additional hazard of an exploding vessel.
A further drawback of the open-circuit system is that it is by nature highly wasteful of oxygen. In the open-circuit system, air from the lungs is not recovered, and the exhausted air typically includes a considerable amount of oxygen. However, the air cannot be reused, because carbon dioxide is present in it and would build up as the air is rebreathed.
Some of these drawbacks have been avoided through the use of closed-circuit systems on Himalayan expeditions. These systems employ means for removing the carbon dioxide in the exhausted air, and the exhaust air can therefore be breathed again. In this manner, oxygen is not wasted, and the user can be supplied with nearly pure oxygen. In addition to saving oxygen, this type of an arrangement makes it feasible to keep the partial pressure of oxygen in the lungs equal to or even greater than the partial pressure that ordinarily obtains at sea level.
Unfortunately, the closed-circuit systems that have been used heretofore have not proved reliable. Few have operated properly for more than a few hours. They tend to be susceptible to various malfunctions, such as the icing up of valves and the contamination of the air supply by the ambient nitrogen. Once a malfunction has occurred, moreover, it normally cannot be remedied satisfactorily in the field.
It is accordingly an object of the present invention to provide simplicity and reliability in a closed-circuit oxygen-breathing apparatus that can easily be serviced in the field.